Cancer cells do not simply appear in bone: they invade, enter circulation, and adapt to a new tissue. This review shows how animal models try to recreate that journey—and where the imitation breaks down. Cancer metastasis is a major cause of mortality from several tumors, including those of the breast, prostate, and the thyroid gland.

Bone tissue is one of the most common sites of metastasis, so the treatment of bone metastases is crucial for the cure of cancer. Disease models must be developed to understand the process of bone metastasis in order to devise therapies for it. Several translational models have been developed, but a compendium on different bone metastatic cancers is currently not available.

This review compiles several animal models, mostly involving breast and prostate cancer, to improve the development of preclinical models. Multiple animal models have been used in clinical research to explore the mechanisms and prognosis of tumor metastasis. Translational models have been used to study the advanced stages of tumor metastases, reveal potential protein targets, and develop metastasis-related treatments.

Fully reproducing human bone metastases in animal models is difficult. By selecting different cell lines, animal strains, and tumor transplantation methods, animal models can be constructed to answer various questions. Basing animal models of bone metastasis on general disease models is unreliable because the etiology of bone metastasis of human and animal cancers is different.

Different cancers have different metastatic targets: mouse breast cancer may preferentially metastasize to the lung, while human breast cancer mainly metastasizes to the bone. Lung tumors may specifically metastasize to the vertebral column, so researchers are required to modify the animal models based on their experiments.

The mouse is the most common animal of choice to construct bone metastasis models. Figure one presents a schematic of the main choices involved in building animal models of bone metastases. It organizes the workflow around cell-line injection methods, animal strains, cell strains, and post-assessments used to evaluate successful bone metastasis, with illustrations of mice, dogs, rabbits, laboratory equipment, and different cell types.

The figure matters because the authors emphasize that no single model captures every genetic mechanism, so researchers must adapt models to the cancer type and experimental question. Both patient-derived cancer tissues and immortalized cancer cell lines are used for transplantation.

Patient-derived cancer tissues show genetic concordance between the clinic and the animal models, and help to establish consistent animal models specific to particular cancer cell lines. These models may face obstacles in the form of ethics and tissue availability.

Cell lines, after several passages, can generate stable primary or secondary cancer sites, and researchers can genetically edit cell lines by using luciferase genes or knocking out certain genes. Table one catalogs commonly used breast and prostate cancer cell lines for modeling bone metastasis, linking each line to its origin, mouse model system, and reported metastatic sites.

Breast cancer entries include MDA-MB-two-three-one, MCF-seven, T-four-seven-D, and four-T-one, while prostate cancer entries include PC-three, LNCaP, and DU-one-four-five. This matters because these readily available lines can reproduce bone-metastatic behavior in animal models, while their different origins and tissue preferences help researchers choose an appropriate experimental system.

In situ injection of cancer cells best reproduces the process of cancer metastasis in the human body. When tumor cells are injected into mouse mammary fat pads, they can be seeded through the vasculature towards the target organs, achieving forty to sixty percent of bone metastases in breast cancer animal models.

To study the function of TIE2, a tyrosine kinase receptor, in osteolytic bone metastasis, Drescher’s team administered both bilateral mammary fat pad injections and left ventricular injections to grouped mice. The correlation between carcinoma in situ and bone metastasis was evaluated to determine whether TIE2 inhibition stimulates dormant breast cancer cells and promotes bone metastasis.

Table two organizes implantation methods for bone-metastasis models by the metastatic process studied, along with their advantages and limitations. Orthotopic inoculation captures primary tumors and invasively distant metastases, while intracardiac and caudal-vessel methods study circulation and metastasis; intraosseous injection focuses on bone metastases but does not reflect the complete metastatic course.

Allografts and xenografts can reflect natural heritability and cellular heterogeneity, but usually require immunodeficient mice and high maintenance. Animal models currently rely on intracardiac injections to realize the process of bone metastasis.

Tumor cells are injected into the circulation through the left ventricle of mice, then go through adhesion, degradation, and migration to finally cause metastases in different organs, simulating bloodway metastasis of tumors. Using intracardiac injections to probe cancer-associated factors in the regulation of tumor bone metastasis has become the preferred modeling approach.

This method was used to show that osteoblastic Niche-derived Jagged1 sensitizes bone metastases, while the bone sialoprotein–avb3 integrin axis functioned significantly more efficiently in cancer cell bone metastasis when integrin was overexpressed. Bone metastasis models using luciferase or fluorescent protein-labeled cell lines allow researchers to monitor tumor development in the bones of living animals.

Oliemuller et al. studied SOX11 effects on cell invasion and bone metastasis using DCIS-Luc cells generated by transducing the cells with luciferase two lentiviral particles. Arriaga’s team bred NPKEYFP mice by crossing NPK mice with the Rosa-CAG-LSL-EYFP-WPRE reporter allele.

That breeding facilitated in vivo fluorescence visualization and quantification of YFP-positive prostate tumors and metastases. The IVIS system can provide more accurate quantitative indicators through fluorescent or bioluminescent readings obtained from tumors. Tumor growth in the bone is typically measured once or twice a week, while osteolytic lesions and abnormal bone remodeling can be assessed visually by X-ray or in vivo microCT.

After MDA-MB-231 cells were injected into the left ventricle of NSG mice, weekly IVIS bioluminescence assays assessed osteolytic lesions caused by bone metastasis from triple-negative breast cancer. MicroCT images showed that NKX2-8-silenced cell lines were more likely to produce earlier bone metastases, while its overexpression delayed metastases, inhibited osteoclast activity, and reduced bone metastatic lesions.

Bone metastasis is a common manifestation of cancer deterioration in the mid and late stages of the disease, but much needs to be understood about invasion from migration to the bone tissue and beyond. Animal models are vital tools in preclinical metastatic experiments that can help identify the key steps in bone metastasis.

The review summarizes experimental animals, cell lines, cell implantation techniques, and evaluation methods used while studying common breast and prostate cancer bone metastases. Immunodeficient animals are used to achieve xenograft growth without eliciting a host immune response, and cell line injection models are effective for studying interaction between cancer cells and the bone microenvironment.

Using mice to study human tumor immunity has its limitations. Differences in bone metastasis pathways between humans and animal models can explain why the success of preclinical treatments is not perfectly reproduced in humans. No single model captures every stage of human bone metastasis.

Instead, carefully chosen cell lines, mice, implantation routes, and imaging methods answer different preclinical questions, while their limitations must remain visible.